This document discusses biomedical systems and various types of biopotentials and electrodes. It covers resting potential, action potential, propagation of action potential, biological signals like ECG, EEG, EMG. It describes different types of electrodes - bio-potential electrodes, microelectrodes including etched metal, micropipette, and metal-film coated micropipette electrodes. It also discusses skin surface electrodes and their uses in ECG, EMG, EEG along with desirable electrode features.

1. Biomedical System
By- Sanju Sah
St. Xavier’s college, Maitighar
Department of Microbiology

2. Unit 2. Biomedical system
2.1 Bioelectric potential
2.2 Resting potential
2.3 Action potential
2.4 Propagation of action potential
2.5 Biological signals
2.6 Electrodes
2.7 Bio-potential electrodes
2.8 Microelectrodes
2.9 Skin surface electrodes

3. 2.1 Bioelectric potential
• Bioelectric potentials are generated as a result
of electrochemical activity in cells.

4. 2.2 Resting potential
• All the higher ionic concentration are blocked by
semi-permeable membrane i.e. Na+ are blocked.
• In living cells at rest there is a difference of about 6
0–90 millivolts (mV) localized on the
surface membrane between the cell contents and
external solution. The inner side of the membrane is
charged electronegatively with respect to the outer
side.
Two types of ionic potential
• Resting potential
• Action Potential

6. 2.3 Action Potential
• When the cell is excited by applying ionic
current to the outer cell, the membrane is no
more barrier to the Na+ ion, higher the
concentration, ion can easily pass inside the
cell.
• The inside of the cell is found to be more
positive than that of outside the membrane
potential in the stage is called action
potential.

10. 2.4 Propagation of action potential
• There are mainly sodium ions outside the cell and
potassium ions inside the cell, also the polarity of the
cell membrane suggests that the inside of the cell
surface membrane is more negatively charged than the
outside.
• As a result, when an action potential is induced, the
influx of sodium ions depolarizing the specific section
of the membrane, this event generates a local current
of that section.
• The action potential is transmitted along the
membrane, down to a region of lower concentration of
the ions.

12. 2.5 Biological signals
• Biological Signals
• Electrocardiogram (ECG):
– Recording of electrical activity of heart.
– The normal amplitude is between 0.1-4mV and its frequency response is upto 100Hz.
– It is used to find the heart rate, arrhythmia and other abnormalities of the heart. It is also
serves as timing reference for the cardiovascular measurement.
– It is recorded by applying surface electrodes at the chest and other reference electrodes.
• Electroencephalogram (EEG):
– A recording of the electrical activity of the brain.
– Amplitide is between 10µV to 100µV and its frequency response is up to 100Hz.
– It is used to obtain the different wave of brain, frequency analysis and other indication of the
brain.
– It is recorded by applying surface, needle and reference electrodes.
• Electromyogram (EMG):
– A recording of the electrical activity of skeletal muscles.
– Amplitude is between 50 µV to 2mV and the frequency response is upto 3000Hz.
– It is used to record the potential to find the muscle related disorders.
– Recorded by using one surface, one needle and one reference electrode.
•

13. 2.6 Electrodes
• Ionic potential are generated due to the ionic
current flow. A device used to convert these ionic
potential into the electric potential is called
electrodes.
Desirable features of Electrodes
– It should not produce any movement artifacts i.e.
noises and disturbances.
– It should be durable to keep over longer period.
– Size and dimension should be appropriate depending
upon the application.

14. Cd : capacitance of electrode-
eletrolyte interface
Rd : resistance of electrode-
eletrolyte interface
Rs : resistance of electrode lead
wire
Ecell : cell potential for electrode
Figure: Equavalent Circuit of electrode

15. 2.7 Bio-potential electrodes
• The mechanism of electric conductivity in the
body involves ions as charge carriers. Thus,
picking up bioelectric signals involves
interacting with these ionic charge carriers
and transducing ionic currents into electric
currents required by wires and electronic
instrumentation. This transducing function is
carried out by electrodes that consist of
electrical conductors in contact with the
aqueous ionic solutions of the body.

18. 2.8 Microelectrodes
• To study the electric behavior of cells,
electrodes that are themselves smaller
than the cells being studied need to be
used.
• Three types of electrodes have been
described for this purpose:
– Etched metal electrodes
• The metal microelectrode is essentially a
subminiature version of the needle electrode
• In this case, a strong metal such as tungsten
is used.
• The advantage of these electrodes is that
they are both small and robust
• disadvantage is the difficulty encountered in
their fabrication and their high source
impedance

19. – micropipette electrodes
• consists of a fine glass capillary drawn
to a very narrow point and filled with
an electrolytic solution.
• The electrolytic solution in the lumen
serves as the contact between the
interior of the cell.
• These electrodes also suffer from
high source impedances and
fabrication difficulty.
– metal-film-coated micropipette
electrodes
• A combined form of these two types
of electrodes

20. 2.9 Skin surface electrodes
– Large surface: Ancient, therefore still used, ECG
– Metal disk with stainless steel; platinum or gold coated
– EMG, EEG
– smaller diameters
– motion artifacts
– Disposable foam-pad: Cheap!